I solved it.
Solution:
I went in to my projects folder in documents and saved the folder somewhere else.
After that i downloaded the project again from epic (sync the map from uefn) and that was a older version of my map where that datalayer file was not broken.
I started uefn and i could indeed launch a session. (validation passed)
Now i deleted the 5X6MCAGRUEK5PRWBOMPU71.uasset and replaced every file in my projects folder to get back where i was before.
That solved the issue for me.